The present invention relates to an optical disc apparatus for recording information on or reproducing information from an optical disc, and to an optical pickup apparatus used for the same. More particularly, the present invention relates to an optical disc apparatus for recording information on or reproducing information from an optical disc that has a plurality of laminated information recording layers, and to an optical pickup apparatus used for the same.
A technology of a multilayer optical disc having laminated information recording layers has been studied as a method of increasing the storage capacity of the optical disc. In the standard of a DVD (Digital Versatile Disc), BD (Blue-ray Disc) and HD-DVD (High Density Digital Versatile Disc), a two-layer optical disc is commercialized in which two information recording layers are laminated at an interval of about 20 to 55 μm. In addition, a three- or more-layer optical disc has also been studied as a technology of achieving a larger capacity.
When recording information on or reproducing information from the multilayer optical disc, it is necessary to eliminate as much as possible the offset of a servo signal such as a focus error signal or a tracking error signal caused by a stray light from other layer.
A method of eliminating the effect due to the stray light from other layer is described, for example, in an article of “Journal of Institute of Electronics Information and Communication Engineers” CPM2005-149 (2005-10), which describes about the placement of a tracking photodetector in a region free of a stray light from other layer.
However, the above article (CPM2005-149 (2005-10)) does not describe about the effect that the stray light has on the focus error signal.
Furthermore, in the above article (CPM2005-149 (2005-10)), it is required to dispose a light receiving part for the tracking error signal outside the stray light from other layer that occurs around the light receiving part for the focus error signal, thus the size of a light detector being increased.
A background art of the optical pickup apparatus is proposed in a Japanese Laid-open Patent Application JP-A-9-223321. In the Laid-open Patent Application JP-A-9-223321, PROBLEM TO BE SOLVED reads as follows: To provide an optical information reproducing apparatus that can be simplified by reducing the number of optical parts, and to provide a method of adjusting the optical information reproducing apparatus that enables the adjustment of a tracking error signal in accordance with the characteristic of an optical disc. SOLUTION reads as follows: The optical information reproducing apparatus comprises: an optical pickup having an objective lens for irradiating the optical disc with light; a first dividing means for dividing a light spot of a light emitted from the optical disc substantially perpendicularly to the direction equivalent to a track to form a light spot on an end region and a light spot on a middle region relative to the center of the light spot; a second dividing means for further dividing the light spots on the end region and middle region in substantially parallel to the direction equivalent to the track of the optical disc; a light receiving element having a plurality of light receiving cells for receiving the light divided by the first and second dividing means; a light spot displacement signal detecting means for computing the outputs of the light receiving cells that receive the light on the middle region divided by the second dividing means to detect the relative displacement of the light spots on the light receiving element; a tracking error generating means for computing the outputs of the light receiving cells that receive the light on the middle region divided by the second dividing means to detect a relative displacement between the track and objective lens; an offset correction means for correcting the offset of the tracking error signal by the computing the output signal of the light spot displacement signal detecting means and the output signal of the tracking error generating means; an objective lens driving device for driving the objective lens in the direction across the track of the optical disc; a tracking control means for drive-controlling the objective lens driving device; and a switching means for switching the input of the tracking control means to the output of the light spot displacement signal detecting means during an access, and for switching the input of the tracking control means to the output of the tracking error generating means via the offset correction means during reproducing of the information of the optical disc.